Sigma 24 mm f/1.8 EX DG
Table of Contents
- Handling and build quality
- Focusing and focusing accuracy
The 35 mm focal length is considered the longest of the wide-angles for the 24x36 mm (FX) format and is a very versatile focal length. For many compacts, the shortest focal length of the zoom range very often gives a field of view similar to what the 35 mm will give on the 24x36 mm format, this is often called the “35 mm equivalent focal length”. The 35 mm gives a very moderate wide angle perspective and is a very good alternative to the “normal” lens (i.e. 50 mm on the 24x36 mm format). It has a hardly noticeable wide angle perspective distortion in many situations while still giving just that extra field of view which often may be sought after for indoor photography or landscapes. In the era of film cameras and fixed focal length lenses, it was not uncommon to choose a 35 mm rather than a 50mm as a “normal” lens for just those reasons. It is therefore not surprising that Nikon has made several high quality 35 millimetres for analog photography, ranging from the fast and highly praised (but not unreasonably priced!) 35 mm f/1.4 to the affordable 35 mm f/2.8, plus special lenses like a macro or a shift lens. The 35 mm f/1.4 AI is still in production, and both this lens, the f/2.0 and the f/2.8 version are available used at decent prices.
Switching from analog 24x36 mm to DX digital, simple math (35 mm/1.5=23.3 mm) tells us that a 24 mm on a DX format camera will give a field of view (61°) practically identical to the FOV of a 35 mm on the 24x36 mm/FX format (62°). Even if Nikon has some very nice zoom lenses, often with vibration reduction, sometimes slow zooms just don't cut it, even with VR. VR stabilises the image against camera shake, but it doesn't freeze subject motion under low light conditions. Thus, there are some reasons for wanting fast (and affordable!) lenses with a fixed focal length in general, and also for wanting a fast and affordable lens with a moderate wide angle and fixed focal length. I've wanted a fast and affordable 24 mm for my D300, so Nikon's lack of fast wide angle lenses with a fixed focal length for the DX format has really bugged me for a little while. Their fast autofocus fixed focal length lenses in the range from 35 mm to 85 mm (two 35 mm, three 50 mm and the 85 mm f/1.8) are great buys giving very good performance in small packages at very decent prices. Thus the lack of a fast and affordable 24 mm is noticeable, as the 35 mm focal length is a normal, not a wide angle lens on the DX format. Their 35 mm f/1.8 G AF-S is even a DX lens, so switching to an FX format body reduces the assortment of fast and affordable wide-angled fixed focal length lenses to only one lens, the 35 mm f/2.0 AF-D. And face it: f/2.0 is just borderline “fast”. In my opinion you ought to have at least f/1.8, preferably even better, to really start talking about “fast” (even though there's only one third of an f-stop between f/2.0 and f/1.8). This is partly due to irrational feelings, partly due to the fact that as a general rule, a lens performs better slightly stopped down than it does wide open.
Early in 2010, Nikon finally launched a new wide angle fixed focal length lens, the 24 mm f/1.4 AF-S, but this lens is clearly targeted towards the professional market at a price way beyond the budget of many amateurs (including myself!). The only relatively fast and at the same time affordable alternatives from Nikon are the small 24 mm f/2.8 AF-D or the somewhat large and bulky (and more expensive!) 17-xx f/2.8 zooms, the latter types also available from third-party manufacturers at somewhat lower prices than Nikon's. The 24 mm fixed focal length could definitely be an alternative, however f/2.8 is not really what one would call “fast”. In addition, the performance on the DX format is somewhat lower than one would want for a Nikon. As Bjørn Rørslett writes, “The 24/2.8 MF Nikon is a classic lens in the Nikon line and one that remains a dependable workhorse to this day. However, on a D2X or D200 and depending on subject, the CA can be quite troublesome and it surely detracts from the overall sharpness of the 24 lens.” Personally, I fully agree with Bjørn Rørslett on this after trying out my old 24 mm f/2.8 AI on my D300 body. It would probably also be an issue for the 24 mm f/2.8 AF-D, as these two lenses share the same optical formula. Of course, the new 24 mm f/1.4 AF-S would solve all such problems, however, one would end up with a quite different problem: How to afford it. Despite all its good qualities, “affordability” is definitely not the word that springs first to one's mind when considering this lens. Even though a 24 mm f/1.4 would be a wonderfully fast, moderately wide-angled lens for the DX format.
When Nikon doesn't deliver the goods (fast, wide-angled and affordable), we'll have to look to third-party manufacturers. Of those, only Sigma has a possible candidate: The Sigma 24 mm f/1.8 EX DG. Sigma calls this a “macro” lens due to its 18 cm close focus limit, but it is of course not a true macro lens. It just has a fairly short close focusing distance. At f/1.8, we get one and a third f-stop more light than with Nikon's 24 mm f/2.8 and only two thirds of an f-stop less than with the 24 mm f/1.4 AF-S . The price is in the same range as Nikon's 24 mm f/2.8, i.e. within the capabilities of your normal, average family guy. One problem with the Sigma, though, is the near complete lack of on-line reviews with real images taken with that lens. Thus, buying one of these may be considered somewhat risky, especially when taking into account the variable reputation of third-party lenses in general.
To rectify the last problem, I decided to write up my impressions after trying out this lens. To put this review into perspective: I am an amateur photographer probably at the decent-but-usually-not-stunning snapshot level and with moderate artistic ambitions. I have been using a camera since my early teens and got my first SLR at the ripe age of fifteen. I've only used Nikon SLRs, have quite recently converted from analog to digital photography, and I still love the tiny, classic MF-Nikons and Nikons for their compactness and almost Leica-like quality feeling. Having a natural science/technology background, I'm fond of using gadgets and reading gadget specifications, and since I often need to crop my images in post-processing for decent composition I prefer lenses that give good sharpness and cameras with high resolution.
Sigma calls this lens «24 mm F1.8 EX DG ASP Macro».
- EX means a better finish on the exterior. This is of course a matter of taste, personally I prefer the classic Nikon semi-matte black finish over the “crinkled” look of the Sigma EX lenses.
- DG means a lens designed for digital use, but with an image circle covering a full 24x36 mm frame. It doesn't really matter too much for you if you're using a small sensor SLR like Nikon DX or Canon EF-S, but an advantage for the crop sensor SLR user is that you will crop out the outermost parts of the image circle, which usually has even lower sharpness than the central parts of the image circle.
- ASP means that it has one or more aspherical elements, claimed to reduce distortion.
- Macro means that the lens can focus to a short distance. This designation is often misused, also for this lens. A true macro lens should be able to focus to 1:1, at least 1:2. This lens has a maximum reproduction ratio equal to 1:2.7 and is thus a close focus lens rather than a true macro lens.
- According to Sigma, it has an internal focusing system and a 9-blade diaphragm. The latter is supposed to give a more pleasant “bokeh”, but as we will see, the effect is moderate.
Here's Sigma's sales pitch:
Sigma’s 24 mm F1.8 EX DG Aspherical Macro lens is a large aperture wide angle lens giving photographers freedom of expression with the ability to set the desired aperture and get as close as 7.1 inches allowing the photographer the juxtaposition between near and backgrounds in the distance. The 84º angle of view is perfect for landscape photos while also great for shooting group shots without distorting the subjects at the edge of the frame and compact enough for working in tight quarter with a single subject. This lens is perfect for photo journalists where it is essential to have a fast, wide angle lens, scenic, social and full-time professional photographers who are in need of a hardworking lens. Extremely compact within the category of super fast wide angle lenses and totally affordable for the professional as well as aspiring professional and student photographers!
At the time of writing (early 2010), Sigma's MSRP is 570 US$, but currently the lens can be bought for about 450 US$ at one of the larger on-line camera stores.
Let us compare The Sigma 24 mm f/1.8 with some more or less realistic alternatives in Nikon's lens line-up (manufacturer's specs are given):
|Nikon 24 mm f/2.8 AF-D||270g||65x46mm||52mm||A bit slow, suboptimal performance on DX. No VR. Manual focus version available. Quite affordable. Won't autofocus on Nikon's low-end bodies.|
|Nikon 18-55 mm f/3.5-5.6 G VR||265g||73x80mm||52mm||Slow, quite decent optical performance, typical kit lens build quality (plasticky). No aperture ring. VR. Very affordable.|
|Nikon 16-85mm f/3.5-5.6 G AF-S DX ED VR||485g||72x85mm||67mm||Slow, good performance, good build quality. No aperture ring. VR.|
|Sigma 24 mm f/1.8 EX DG||485g||84x83mm||77mm||Fast, price comparable to Nikon 24 mm f/2.8, size comparable to Nikon 16-85/3.5-5.6. No VR. Won't autofocus on Nikon's low-end bodies.|
|Nikon 28mm f/1.4 AF-D||520g||75x78mm||77mm||Very fast, very expensive, only available used. No VR. Won't autofocus on Nikon's low-end bodies.|
|Nikon 24 mm f/1.4 G AF-S ED||620g||83x88mm||77mm||Very fast, very expensive. No aperture ring. No VR.|
|Nikon 17-35 mm f/2.8 D AF-S IF-ED||750g||82x105mm||77mm||Somewhat slow, big, expensive. No VR.|
|Nikon 17-55 mm f/2.8 G AF-S DX IF-ED||750g||85x110mm||77mm||Somewhat slow, big, expensive. No aperture ring. No VR.|
|Nikon 14-24 mm f/2.8 G AF-S ED||970g||98x132mm||none||Somewhat slow, really big, expensive. No aperture ring. No VR.|
The Sigma 24 mm f/1.8 is both bulkier and heavier than Nikon's 24 mm f/2.8, but as is evident from the photo below, it is very comparable in size to e.g. Nikon's 16-85 mm f/3.5-5.6 AF-S.
Handling and build quality
Since the Sigma 24 mm f/1.8 is comparable in size to Nikon's 16-85 mm, it is not surprising that it handles quite well on a prosumer grade body like the D300. On the consumer-grade bodies like the D60 or the D90, it would probably feel a bit on the large and heavy side. Note, however, that the Sigma doesn't have a servo focus motor and will not autofocus on Nikon's low-end bodies like the D40, D60, D3100 or D5000. On a small analog SLR body like the FE2 or the FM3a, it will definitely be on the large and heavy side and doesn't balance particularly well.
It looks quite good and gives a more solid impression than e.g. Nikon's low-end kit lenses, but it has a slightly clunky feel to it. On the positive side, it comes with a bayonet-style lens hood, real front and rear covers and a quite decently-looking lens case, which, incidentally, has just enough room for a Nikon 16-85 mm with a reverse-mounted lens hood if you are in a pinch. The aperture collar rotates in the right direction, while the focusing collar rotates in the wrong direction (for a Nikon user).
Focusing and focusing accuracy
One of the great disadvantages of third-party lenses is the fact that the focusing collar usually rotates in the wrong direction. In the manual focus days, Canonians used to claim that it was Nikon's focusing collar which rotated in the wrong direction, but every intelligent person will of course know that this is a grave misunderstanding on the Canonians' side. Fortunately, this problem was greatly reduced when AF came to the rescue, and these days the challenge of adjusting focus quickly and without turning the collar in the wrong direction is handled by the camera. The Sigma 24 mm f/1.8 has no AF clutch, so the user switches between AF and MF by pushing or pulling the focus ring. If you can live with a focus collar which rotates during AF, like Nikon's own AF-D lenses, it is possible to keep the collar in the MF position. The lens will still autofocus.
Sigma has a certain reputation of laxer quality control than e.g. Nikon, so focus accuracy is of course the first thing to check for. There are a number of strong and conflicting opinions on the web on how to check focus accuracy, but I solved the challenge of knowing if I did the right thing by using exactly the same setup and focus point with both the new Sigma and a lens which I trusted. In my case, that was my Nikon 16-85 mm VR, zoomed to 24 mm. My copy of the Sigma definitely had a front focus problem and was promptly returned to the store for adjustment. Since it apparently was not possible to adjust the focus on this lens and since the store manager was more than a little reluctant to order a number of copies of the lens to find one that gave good focus, I made a deal with them: If the AF fine-tuning system of my D300 was able to handle the front-focus problem of the lens, I'd get it at a reduced price. Fortunately, most of the focus issues could be resolved by in-camera adjustment, and only a slight tendency to front focus was apparent at short distances. This was not considered a big issue, since the lens anyhow showed quite mediocre performance at short distances and thus would not be used as a close-range/semi-macro lens. In addition to the front focusing issue, a marked longitudinal chromatic aberration was visible at short distances (below 30-50 cm).
From an economical point of view, one of Nikon's 24 mm f/2.8 lenses can be considered the only real alternative to the Sigma. The two lenses (24 mm f/2.8 AF-D and the manual-focus 24 mm f/2.8 AI) share the same optical formula, and it is reasonable to assume that they also have similar performance. Both Nikon and Sigma are publishing MTF charts on their websites. I have taken the liberty of reproducing those charts in my review, even if MTF charts don't tell the whole story.
Judging from the MTF charts, the sharpness of the two lenses should be very similar. It should therefore be theoretically possible to match the wide-open performance of the 24 mm Nikon with one and one third of an f-stop more light falling on the sensor.
As mentioned above, the lens showed some ugly colour fringing at close distances and maximum aperture. However, since close-up photography was not the intended use for the lens, performance at more normal distances was considered more interesting. Thus, I headed downtown to try it under (for me) more normal conditions. At smaller apertures, there is a number of alternative lenses to choose between, notably the Nikon 16-85 mm f/3.5-5.6 G AF-S DX ED VR which in my opinion is a great walk-around and travel zoom with very good performance. However, even at 16 mm, the maximum aperture of the 16-85 mm is only f/3.5. That is two full stops slower than the Sigma. So, large aperture performance was the main attraction of this lens for me. I did try out a couple of pictures at f/8, however, to see how the lens behaved at more optimal conditions. Having access to only one digital SLR able to autofocus old-fashioned screwdriver-type lenses, I've only tested this lens on my own Nikon D300.
All images were recorded as Nikon NEF (raw file format) and post-processed in Adobe Lightroom 2.6. Colour balance, exposure, contrast etc. was determined individually for each picture, but all images were capture sharpened using Lightroom's built-in “Landscape sharpening” preset to get comparable results. The 1:1 crops are of course not re-sized, the other images were re-sized in Lightroom to 800 pixels along the longest edge, and all images (both the re-sized ones and the 1:1 crops) have been output-sharpened “normal, for screen” in Lightroom.
Initial impressions and bokeh
This picture was cropped to 4:3 format, mostly at the top. The low-resolution image looks decently sharp, but then almost anything should look decently sharp when down-sized to 600 by 800 pixels. The bokeh, while quite far from stunningly beautiful, fortunately isn't downright ugly.
Let's take a closer look at the lettering on the top of the garbage can. This is a 1:1 crop taken roughly two thirds of the distance from the centre to the long edge of the full frame, and about halfway between the centre and the top edge of the full frame. Not too bad, eh? I've corrected some lateral chromatic aberration during post-processing in Lightroom. There are more details about that further down in this little amateur review.
Another image showing good sharpness not too far from the centre, and also fairly decent bokeh. f/1.8:
A black and white shot, showing the quite nice moderate wide angle perspective we get on the DX sensor from the 24 mm focal length. f/1.8:
Now to something a little bit more demanding. I found these bars in front of a store which had closed for the Sunday:
Let's overlook the fact that I wasn't dead straight on the bars and thus got a pinch of Keystone effect into the image. Here, barrel distortion is the issue. Although fairly moderate, the distortion definitely doesn't look too good. I failed to correct it fully in Photoshop. There's a moustache-like wave to the distortion which is pretty hard to correct. Oh well, this baby ain't going to be my architecture lens anyhow.
Sharpness and chromatic aberration full open
Let's look more closely at the image. A flat surface with a sharp, contrasty pattern is one of the better image types to use for judging sharpness and chromatic aberration. First, 1:1 crops without any CA correction.
The centre shows good sharpness even at f/1.8. Not surprisingly, the edges are noticeably softer, and the corners are no good at all. According to rumours, Sigma optimises their lenses for centre sharpness and lets the corners fend for themselves, and this picture seems to be a good illustration of just that. CA is clearly visible, especially at the edges. I've got a slight suspicion that the corners are so soft that even CA is somewhat blurred out. Fortunately, the CA is fairly easily corrected in Lightroom, and I've already made myself a develop preset for the CA correction value.
The CA correction seems to make the centre of the image a tad softer, but the quite harsh red/green fringing at the edge has disappeared. The CA wasn't very troublesome at the corner anyhow, due to the softness, but what could be seen has also been corrected quite nicely. So, more or less as expected, the lens is quite soft at the edges and especially in the corners at full aperture. I don't even want to think about how it will perform at the edges and corners of an FX sensor, as this is an FX image circle lens and using it on a DX sensor camera we are already approaching the “sweet spot” with regard to sharpness.
Sharpness stopped down
Now, what about the performance at smaller apertures? As I've already argued, this is a lens which I'm planning to use at large-to-wide-open apertures, but it would be nice if it could deliver good results at a more optimal aperture. In this picture, I've focused on the top of the crane, but the centre of the image clearly lies within the DOF range.
From the 1:1 crops we see that at f/8, the situation improves quite markedly, and even close-to-corner sharpness is quite good.
The Sigma 24 mm f/1.8 EX DG delivers good results in the centre even wide open. For low-light situations, it is quite usable provided you don't need high edge or corner sharpness. Lateral CA is pronounced, but can be corrected quite well in post-processing. It delivers poor results at short distances, and the “macro” designation given by Sigma should definitely be neglected. At medium to long distances and not too far from the centre of the image, however, it delivers quite good results, especially when stopped down. Given the price, it is definitely an alternative to Nikon's own 24 mm f/1.4 or the discontinued 28/1.4 for wide-angle DX shooting in low light. However, be aware of front focusing problems unless your camera body has the capability to correct autofocus errors. Regarding size, it is quite comparable to e.g. the Nikon 16-85 mm f/3.5-5.6 AF-S and handles well on one of the larger camera bodies like the D300. It does not have an internal focusing motor and will not autofocus on Nikon's lower-end bodies. At the MSRP and if I didn't really need (or rather want!) the large maximum aperture, I'd probably rather buy the Nikon 24 mm f/2.8 which performs just as well at a lower price and in a much smaller package, but the Sigma is a very decent alternative provided you think that you need the extra one and a third f-stop.
If you are looking for a fast wide-angle with a fixed focal length for the Nikon DX format, I would recommend this lens as an economically realistic alternative to the Nikon 24 mm f/1.4 AF-S. It delivers two full f-stops more light than the standard walk-around zoom at its shortest end and one and a third f-stop more light than the 24 mm f/2.8 and the “fast” f/2.8 zooms from Nikon and third-party manufacturers. Be, however, aware of the limitations in terms of edge/corner sharpness and chromatic aberration. And don't forget to check your copy of the lens for focusing errors!
Copyright © 2010 Størker Moe. All rights reserved.
All text and all images are © Størker Moe (unless otherwise indicated) and may not be reproduced or used in other works without explicit written consent of the author